This painting is based on the Book of Tobit which tells the story of Tobit of Nenevah. Tobit is described as a man of good faith who suffers from blindness and poverty. He sent his son, Tobias, to a distant city to collect money he had deposited there, and hired a companion to accompany the youth. The companion was actually the archangel Raphael in disguise. Their journey was successful: not only was the money recovered, but medicine made from a monstrous fish Tobias encounters along the way cures Tobit's blindness.

In Hebrew, Raphael's name means "God has healed." In this painting, Raphael holds a golden mortar used for compounding medicinal ingredients. Although the archangel is usually shown with a mortar or medicine box, his identity here is established by the presence of Tobias holding a fish. Raphael is named only in the Book of Tobit.

The story of Tobit may have been particularly popular in fifteenth-century Florence because of its appeal to merchant families, whose sons were often sent to trade in far-away cities. Paintings of Tobias and his angelic guardian were likely commissioned as dedications to ensure a safe journey, or offer thanks for a safe return. The painting's suggestion of reward for fair dealing may have been equally welcome.